1) 
var i,n,k:integer; nf,kf,nkf,c:real;
begin
write('n='); readln(n);
write('k='); readln(k);
nf:=1;kf:=1;nkf:=1;
for i:=1 to n do nf:=nf*i;
for i:=1 to k do kf:=kf*i;
for i:=1 to n-k do nkf:=nkf*i;
c:=nf/kf/nkf;
writeln('c=',c);
end.
2) 
var a,s:real; n,i:integer;
begin
write('a='); readln(a);
write('n='); readln(n);
s:=1;
for i:=1 to n do s:=s+i*a;
writeln('s=',s);
end.
3) 
var n,i,s:integer;
begin
write('n='); readln(n);
s:=1;
for i:=1 to n+1 do s:=s*2;
s:=s-1;
writeln('s=',s);
end.